The intermediate or "Series J" actions were Savages 1st attempt at a Short action and have a screw spacing of 4.52". Since your action is in 30-06, it is a Long action with the 5.06" spacing.
Chances are its a Staggerfeed model. If it is a flat rear then it most certainly is a SF. If you want to know how to tell the difference, read this ARTICLE and it will show you how.

Yes you should be able to build a 260 on it with minimal difficulty.

As long as it is a post 1966 (IIRC) model then it should accept most any of the aftermarket triggers out there. You can even retro fit an Accu-trigger if you want.